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RE: fibermesh rates - Performance-Based Concrete...

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I'd like to further discuss my post about performance-based concrete specs later this evening when not at work, but I'd like to state, respectfully, that I'm not on the same page as Mr. Sprague when it comes to the issue of concrete reinforcement.  This simply could be a function of our geography.  Anyhow, more later to build on the rest of Harold's post, which I was glad to see.  I'd also like to say DO I agree with Harold's stance on the use of fibers in slabs (at least without REAL reinforcement in there also).
 
-Ben Maxwell

Jerry Coombs <JCoombs(--nospam--at)carollo.com> wrote:
Should we also do that with WWF and #3 T&S reinforcement?  Fibers have their limitations just like and bar reinf.
 
Location (geographical) is everything with SOG's, and I may have had ideal conditions, but never ran into any cracking issues.
The slabs MUST be cut with a Soff-Cut saw as soon as possible, and MUST have relatively close spacing of control joints.  Did you still have probs with those req'ts pretty tight?
jdc

>>> On 2/13/2008 at 1:43 PM, Harold Sprague <spraguehope(--nospam--at)hotmail.com> wrote:
Ben,
 
You raise an excellent point.  Give the performance requirements to the concrete slab contractor, but include your expectations on cracks (size and frequency) with a set of drawings.  Also require him to perform no cost repairs for 2 years.  Define the repairs that are acceptable.  Require a lot of bonding (deep pocket).  Let them prepare the subgrade, develop a mix including reinforcing, means of crack control for both drying and plastic shrinkage cracking, curing, and maintenance plan. 
 
The people like Kalman who have constructed industrial floors for decades for any loading condition will only use rebar for crack control.  That should serve as a warning.  Kalman is one of those contractors that constructs it all and warrants it all.  
 
Anyone doing a search on the SEAINT archives will know my experience with cracking of slabs using polypropylene fibers, the cost of repairs, and the law suits that result.  As the archive suggests, I am not an advocate of polypropylene fibers.  

Regards,
Harold Sprague



From: spraguehope(--nospam--at)hotmail.com
To: akester(--nospam--at)cfl.rr.com
Subject: RE: fibermesh rates - Performance-Based Concrete...
Date: Wed, 13 Feb 2008 19:40:25 +0000

Ben raises an excellent point.  Give the performance requirements to the concrete slab contractor, but include your expectations on cracks (size and frequency) with a set of drawings.  Also require him to perform no cost repairs for 2 years.  Define the repairs that are acceptable.  Require a lot of bonding (deep pocket).  Let them prepare the subgrade, develop a mix including reinforcing, means of crack control for both drying and plastic shrinkage cracking, curing, and maintenance plan. 
 
The people like Kalman who have constructed industrial floors for decades for any loading condition will only use rebar for crack control.  That should serve as a warning.  Kalman is one of those contractors that constructs it all and warrants it all. 
 
I have had enough experience with polypropylene suppliers to know that the suppliers will make a lot of performance claims but will balk at accepting any responsibility when the slab cracks.  Anyone doing a search on the SEAINT archives will know my experience with cracking of slabs using polypropylene fibers, the cost of repairs, and the law suits that result.  As the archive suggests, I am not an advocate of polypropylene fibers. 
 
Polypropylene fibers will reduce the number of cracks in a slab, but not the rate of concrete shrinkage.  That should serve as a warning.  The slab cracks will be larger reducing aggregate interlock and will result in differential curling which will cost about $6 per lineal foot to repair. 
 
I have been a part of too many law suits to trust polypropylene suppliers.  Masterbuilders has lousy research in this area, but they have great lawyers. 

Regards,
Harold Sprague



Date: Wed, 13 Feb 2008 10:07:19 -0800
From: enginerd666(--nospam--at)yahoo.com
Subject: Re: fibermesh rates - Performance-Based Concrete...
To: seaint(--nospam--at)seaint.org

This is a classic example of why concrete should be packaged by engineers as a performance-based product.  The concrete industry has changed so much in the past few decades, and so much has changed in terms of material options, aggregate availability, the myriad of admixture products, and so on, that it really requires a exacting command of concrete science to proportion a mix.  Increasingly so, this is NOT the engineer's realm.
 
Does specifying a prescriptive mix really matter in terms of structure?  In general, we want concrete of a certain strength and weight.  More specifically, we may want concrete with low shrinkage and/or concrete with a certain air content.  Very specifically, for exacting applications, we could need concrete with low porosity, high corrosion resistance, or controlled heat of hydration (mass concrete).
 
Who is more qualified to determine the materials, proportions, delivery methods, placement methods, and curing of concrete that meet a set of qualifications, the engineer, or the concrete producer?  I argue the latter.
 
We care about the qualities of the end product.  How it gets there should not be the responsibility of the engineer.
 
We're not on the hook to determine the exact amount of carbon in a heat of steel.  We simply specify the appropriate ASTM standard for the material we want.  Wood is similar and we don't need to tell CMU manufacturer's how to make their masonry - just that it meets the appropriate ASTM standard.  Why is concrete so out of bounds with respect to the other major building materials?  Why should it be?
 
It should be up to the concrete producer to provide, deliver, and place satisfactory concrete material in conformance with a set of engineering performance requirements.  We just need to establish and standardize the performance requirements.
 
Performance specification of concrete gets tricky in terms of shrinkage control, permeability, and mass concrete, but there are tests and practices established, in-place, tested, and in use that have demonstrated that it is possible to use a performance-based methodology.
 
Not to get too long-winded about this, but we should not be hung out to dry because of issues like Andrew's where the contractor can easily pass blame and the responsibility for bad concrete rests on our shoulders.  I'm sure every engineer on this list can recount scores of stories about being coerced and jostled into making decisions about concrete mixes beyond their true ability to fully realize the consequences.  We shouldn't have to roll dice.
 
-Ben Maxwell
 

"Andrew Kester, P.E." <akester(--nospam--at)cfl.rr.com> wrote:
Listers,
We normally have a fibermesh mix of 3.5lbs/CY of 1.5" polyprop. fiberson our standard SOG in lieu of WWF. We have never had a comment before, but now a GC wants to use less "because his concrete company cannot provide that much and can I use less...?."
 
We are getting this info through the client so we don't know what exactly that means. All the fibermesh specs I have looked at online say 1.5lb/cy MINIMUM.
 
What do you guys use if you don't mind me asking?
 
 
Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Ave., Suite 301
Orlando, FL 32803
M 407-921-1617
F 321-249-0349



Benjamin H. Maxwell, S.E.
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Benjamin H. Maxwell, S.E.


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